Kansas 2044. Time travel will be invented in 30 years' time and quickly made illegal. It will be used only by criminal gangs to send targets back to Loopers, cold-blooded killers employed to murder decades away from detection. The victim arrives out of thin air, hands tied, head covered. The Looper pulls the trigger, collects his cut of "silver" – brickettes of precious metal attached to the mark's back – and burns the body. Once in a blue moon the target arrives strapped in gold – the first sign that the Looper's contract has been terminated. He rolls the body over, takes off the mask and confirms that he's killed himself. His loop's been closed.

Rian Johnson's sharp, smart sci-fi thriller runs on such bizarre ritual. Delayed suicide is part of the cycle for Loopers like Joe (Joseph Gordon-Levitt), who's eager for the chance to tap out and enjoy his last 30 years as he wants. His life until then is locked in a well-worn circuit – an assassination, steak and eggs at his favourite diner, a quick flirt with the waitress, then the trip to the city with the same clubs, the same drugs, the same girls. Around him the economy has flatlined. Only Joe and his kind – well paid, stylish, arrogant playboys – have the money to zip around in sleek flying machines.

Joe's expecting to meet and kill himself. It's only when his older self (Bruce Willis) escapes assassination that the system is undone. Joe senior has seen the future, likes where it leads and doesn't want to give it up. Joe junior, mindful of the punishment that's dealt out to renegades by his boss (Jeff Daniels), needs to track him down and finish the job.

From there, Johnson hauls us through a cat-and-mouse chase, peppered with great dialogue and two showcase performances from Willis and Gordon-Levitt, who's nailed the pained look of befuddlement, the mannered slouch in the walk, that made Willis a star. Even when Johnson winds down their screentime to make room for a side story featuring a prairie mom (Emily Blunt) and her mysteriously gifted son, Looper still ticks along.

Johnson's debut, Brick, asked a lot of its audience, incited you to keep up. Those who found his noirish high-school murder mystery too portenteous might struggle with Looper. At its best, it's a similarly dense film. But, once you commit to the lexicon – to the blunderbusses, the silver, the loops that close and the loops let run – you're in for a breathless ride. It's been a patchy summer for sci-fi, absent of anything that really sticks in the mind. Johnson's deep, distinctive film plays on repeat.